In industry, and in particular in the brewing, distilling and soft drinks industries, the progress of a particular process taking place in a solution is often monitored by measuring the concentration of a solute, for example ethanol, in the solution.
At present, in order to measure the concentration of a solute in a solution a sample of the solution must be taken and analysed. Thus, close monitoring of a process requires samples to be taken at regular intervals. Sampling is time consuming and in many circumstances it is inconvenient to remove samples from solutions while the process is taking place.